What just Happened?

So this guy at work and I have been flirting for weeks. It was great! Texting all the time! We were all set up to watch a movie at his place... then the day before he got word that he could be transferred for his dream job and anytime.
So when I come over he is in the midst of packing up his stuff.
As we watch the movie things progress and we have sex (awkwardly). He mentions he thought I was cute for a couple months and I said (cheekily) I was "a bit fond of him". He mentions he is sad he is leaving and wishes he had a year (the topic of him being sad he is leaving comes up multiple times in the evening).
We fool around (awkwardly) and I mention we can still "have fun" until he leaves.
Later , he turns cold and is on his phone. I mention that I should go and start preparing to leave (taking back the beers I brought) he mentions we could enjoy those another time. We quickly finish off the cheesecake I brought and I mention I enjoyed his company, to which he responds with something irrelevant.

We have a long kiss goodbye and I leave.

Wtf just Happened? Should i just avoid him all together?
What just Happened?
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